Tanning of skins and hides



- Patented Dec. 29, 1925.

JOHANNES HELL, OF ESSLINGEN, GERMANY.

TANNING OF SKINS AND HIDES.

Ho Drawing.

Toall whom it may concern."

Be it known that I, JOHANNES HELL, a citizen of the Republic of Germany, and resident of Esslingen, \Vurttemberg, Germany, have invented certain new and useful Improvements in or Relatin to the Tanning of Skins'an'd Hides, of w ich the fol-- lowing is a specification.

The present invention relates to an improved process of tannin hides and skins under which I also inclu e those in a partially tanned condition.

According to the present invention hides or skins are tanned by means of soluble magnesium salts (such as the sulphate or the chloride) and soluble carbonic acid salts (such as the carbonate or bicarbonate of sodium) in the presence of water. magnesium salts and the carbonic acid salts of other bases may in this process be employed either simultaneously or successively. For instance in the working of this process, the wet hides or skins may be introduced into adrnm, and a mixture of dry magnesium sulphate and sodium bicarbonateis then added. The moisture in the hides or skins as usuall re ared, will in certain y l; P

cases be found su cient to dissolve the salts and render them active; or the hides and skins may be drummed in a solution of magnesium sulphate, and sodium carbonate or sodium bicarbonate added thereto subsequently; or the hides and skins may first be drummed in a solution of carbonate or bicarbonate of sodium and the magnesium sulphate added afterwards.

My improved process is a true tanning process as distinguished from a liming process.

I am not prepared to state with any de-.

gree of certainty what chemical changesleading to the formation of leatheroccur between the soluble magnesium salts, the soluble carbonic acid salts of other bases and the hide substances, but the latter undoubtedly plays an important part. In all probability the tannage which occurs, re-

sults from a precipitation in and upon the hides 0r skins, of one or more insoluble magnesium compounds which are either salts of carbonic acid or contain such salts. In order to secure the best results it is necessary to incorporate a certain minimum quantity of the magnesium carbonate in the skin, and preferably in concentrated solution. It is also important for the securing The Application filed August 29, 1921. Serial No. 496,597.

of the best results that the product should not be washed immediately after removal from the bath, as apparently the reaction continues for several hours, or the reaction roducts do not become fixed at once. hatever may be the exact changes, the fact remains that the hides or skins under 0 a change and. leather is produced w ich leather remains permanent and cannot be reconverted into the condition of a skin, even though the tanned hides or skins be washed,

- for example, with water a few hours after the treatment.

I My tanning process may be'performed in a very short time compared to that required for most tanning processes, and the mate-.

rials used are inexpensive *and easily obtained. The leather obtained may be sold and used without further tanning operation, or the character of the leathers obtained with this improved process ma be greatly varied or modified by the app ication in conjunction therewith or thereafter of tanning processes or substances already known. For example, valuable results may be attained if the hides or skins in addition to being treated by the above process are also subjected to the-action of other'tanning agents such as cellulose extract, formaldehyde, metallic or other tanning salts or other tanning substances.

These substances may be used upon the hides or skins by themselves or in admixture one with the other or after one another at any time in proper con'unction with the magnesium tannage a ove referred to. They may also be used during or after the currying of the leather.

In certain cases, for instance, where vegetable tanning methods are used, the magnesium tanned leather must be .freed from excess of alkali, but in other cases the tanning agents may be added during the process of th magnesium tannage. 1

The following examples are only a few actual methods for carrying the invention into effect. I 1. 100 kg. of unhaired hide are worked for 4 to 6 hours, or longer if necessary, with a concentrated solution containing 21-22 kg. of magnesium sulphate and 7 kg. of sodium bicarbonate .or 9 kg. sodium carbonate, in a drum. The solutions may be prepared either before or after the hides are introduced into the drum or the hides may first of all be brought into the magnesium sulphate solution, and the carbonate or bicarbonate solution added subsequently, or vice versa. The leather thus obtained may be rinsed and then oiled. The resultant product is soft, tough, and of en larged area.

2. The hide treated according to Example 1 is pressed out or exposed to the air, then coated or brushed over with cellulose ex-' tract (purified cellulose sulphite liquor) and thereafter rolled and greased. The leather thus obtained possesses considerable body and retains the form which it is given during staking or currying and does not shrink any further. Similar advantages may be obtained, if an appropriate quantity of celextract is added to the tanning mixremains fiat after cooling, as well as liant,

tough or stable in'grain. Even i such leather has been dried without greasing,

it'will not crack when. subjected to strong bending.

The currying of such leathers may be carried out with or without cellulose extract. The greased leather is particularly tough and strong in the grain; it can readi- Y ly be curried to any grain, thereby dispensing with the otherwise usual softening operations.

4;. Bysteepin the leather obtained in accordance with "xample 1, in dilute formaldehydesolution, or coating it with such solution or with fat, grease or the like to which formaldehyde has been added, the leather attains amongst others, the property valuable or the roductionof imitation rain leather, so t at the graining pro-, duce for example, by plating or emboss-f: ing, is extremely durable. After drying, the graining thus produced cannot be removed permanently even by rolling or pressing the leather with hot plates.

5. If to the tanning mixture described in Example 1 an aqueous solution of 5 kg. of

chrome alum is added, or if the leather obtained in accordance with Example 1 is treated afterwards with "a chrome tanning liquor, a leather is obtained which in addi tion to the good qualities obtained through the magnesium tannageVhas also the characteristics of chrome tanning. Inithe place of chromium salts the partly or com letel prepared leather can also be treate wit j other salt-solutions, such as salts of iron,

' zinc or barium.

'6. By suitable joint application of com erties of those tanned with vegetable su is treated in the fimshed'state with for- 'paratively small quantities of Va etable tanning materials, the leathers obtalned by the "magnesium tan'nage. can be given the pro stances. For example, by the addition of 1 70 litre of oak extract of 20 to 25 B6. to the tanning solutions of Examples 1 or 3, leather is obtained which appears internally and externally like leather tanned with vegetable material. By an re-tanning process leather of any usua leather-shade may be obtained which according to' the mate rial and method of re-tanning used, will produce either firm or soft leather and the substance of theresulting leather may be varied.

7. By alternately treating the skins in different. baths, particular products can be attained. For example, a full bodied leather firm and unbreakable on its grained si e can be obtained, without even greas- I ing, if the hide tanned in accordance with Example 3, is placed for some hours in milk of lime and then further treated as lIl,EX- ample 1.

8. Leather which has been obtained accordin to the treatment given in the above cxamp as, with the exception of the treatment with formaldehyde and chrome salts,

maldeh de, for example by coating with formal ehyde solution thereon. By this means. previous artificially obtained unevenness of the leather is made unremovable.

As the fleshy side of the hides during tannin according to this invention becomes finely grained and smooth, the process is particularly suitable for the tanning of split skins. Their finished appearance is better than with other tanning processes. Artificially obtained grainings cannot be removed after the com letion of the tanning.

In tanning hides in the hair, the invention gives the advantage that when for example formaldehyde is used, such hides are no quickly penetrated by the mixture.

.1 The leather produced by the magnesium tannage. supplemented by another tanning process may have 'all the qualities of a leather produced b the previously known 1!! process alone, but t ere is great economy in time required, and in the quantity of the tanning material required for the supplemental process. a

Having thus described my invention, what I claim as new and desire to'secureby Letters Patent is 1. The process oftanning skins or hides, consisting in.,incorporating carbonic acidsalts of" magnesium within the skins or 12a hides, and in suflicient quantity to effect tannin action.

2. T e process of tanning skins or hides, consisting in treating them with materials capable of forming magnesium carbonates pound in the presence of the hide or skin to be tanned.

5. The process of tanning which includes the drumming of the moist hide or skin in the presence of a magnesium salt and a carbonic acid salt of another base, such salts being soluble in water and in sufiicient quantity to effect tanning action.

6. The process of tanning hides or skins consisting in treating .the hides or skins 'with substances capable of forming 1nsoluble compounds of magnesium -1n the presence of the hides or skins, whereby such insoluble compounds are incorporated in the body of the skinv in an amount sufficient to produce tanning action.

7 The process of tanning hides or skins consisting in treating substances which react in the body of the skin to produce carbonates of magnesium hides or skins the hides or skins with I in a suflicient quantity to produce the tanning action.

8. The process of tanning a hide or skin, consisting in treating the hide or skin with a soluble magnesium salt and a soluble carbonic acid salt of another base in the presence of water, and varyin the charactor of the leather so produce by further tanning by another process.

9. The process of tanning a hide or skin consisting in treating the hide or skin with materials capable of forming magnesium carbonates within or in the presence of the hide, and with formaldehyde.

10. As an article of manufacture leather produced by the interaction of a soluble carbonic acid salt and a soluble magnesium salt in the presence of the hide or skin, and having a product of such action incorporated therein.

11. In the manufacture of leather from hides or skins, the step of preparing the hide or skin for a final tannin action, which preparatory step includes t e treating of the hide or skin with substances reacting to form a substantially insoluble magnesium salt within the structure of the hide or skin.

In testimony whereof I have signed my name to this specification.

J OHANNES HELL. 

